A Taylor polynomial of order nn for a function ff at a point aa is the polynomial Tnf(x)=∑j=0nf(j)(a)j!(x−a)jT_n f(x)=\sum_{j=0}^n \frac{f^{(j)}(a)}{j!}(x-a)^j, assuming the needed exist at aa.

Taylor polynomials package derivative data at a point into a single that locally approximates ff. The approximation is quantified by .

Examples
  • For f(x)=exf(x)=e^x at a=0a=0, Tnf(x)=∑j=0nxjj!T_n f(x)=\sum_{j=0}^n \frac{x^j}{j!}.
  • For f(x)=sin⁡xf(x)=\sin x at a=0a=0, T2n+1f(x)=∑j=0n(−1)jx2j+1(2j+1)!T_{2n+1} f(x)=\sum_{j=0}^n (-1)^j \frac{x^{2j+1}}{(2j+1)!}.